System for the detection by a motor vehicle of a phenomenon that interferes with visibility

ABSTRACT

A process for the detection from a vehicle of a visibility interference phenomenon, comprising the following steps: the emission of a beam of light to illuminate the rear of the vehicle, the beam of light being emitted into a field of vision of a camera mounted in the vehicle, and the determination of a presence and the nature of a visibility interference phenomenon on the basis of at least one image captured by the camera.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to French Application No. 0705715 filedAug. 3, 2007, which application is incorporated herein by reference andmade a part hereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for detecting a phenomenonthat interferes with visibility and a detection device allowing thisprocess to be implemented.

It will be used in particular in the sphere of motor vehicles.

2. Description of the Related Art

In the case of motor vehicle applications, processes are already knownunder the state of the art, whereby the presence of a solid obstaclesuch as a vehicle following closely behind can be observed and a warningcan be given if this vehicle gets too close. Such systems work forexample on the basis of a distance sensor. In the event of such anobstacle being present and provided that the rear lights are switchedon, on a wet road (regardless of whether it is actually raining or not),the visibility of the lights can be affected by a visibilityinterference such as spray of water produced by the rear wheels of thevehicle or the driver of the vehicle behind; this can be the cause ofconcern for the driver following and also for the driver being followed.However, such processes do not enable a visibility interferencephenomenon to be detected.

Such detection devices are also known. For example, EP 1 715 456, whichis equivalent to U.S. Patent Publication 2007/0031006, which isincorporated herein by reference and made a part hereof, describes aprocess for detecting evening fog along a road in front of a vehicle,comprising a system for illuminating the roadway with the vehicle'sheadlights. Such systems work on the basis of capturing a series ofimages of the roadway, extracting a halo of light from these imagescreated by the headlights, comparing this with the nearest ellipticalcurve and deducing the presence or the absence of fog.

The document EP 1 498 721 describes a fog detection process, comprisinga numerical camera, which scans the environment around the vehicle andan imaging system, which compares the luminosity of each pixel of thecamera to a predetermined value and then deduces the presence of fog ifthe luminosity of any of the pixels is lower than the said predeterminedvalue.

The document EP 1 298 481, which is equivalent to U.S. Pat. No.6,803,574, which is incorporated herein by reference and made a parthereof, describes a night vision device, comprising an infra-redemitter, a detector and a display device. The emitter comprises one ormore pulse emitting diodes, which are operated by a driver, whichoperates simultaneously the detector or a camera. This document does notcover fog applications.

The document EP 1 553 429, which is equivalent to U.S. Pat. No.7,350,945, which is incorporated herein by reference and made a parthereof, describes a system for detecting traffic conditions on a roadway(both weather conditions and the detection of obstacles), which ismounted on a motor vehicle and comprises at least one light projectorhaving a first light source emitting a visible beam of light and atleast one source of modulatable light, in particular at a highfrequency, emitting a beam of infra-red light along the road ahead andat least one camera able to capture images of the road ahead.

The document “Fog lamp automation with visibility sensor, the next stepof lighting automation”, by J. Lelevé et al., appearing in the VDIReport No. 1907, 2005, describes a passive fog detection system, basedon cameras and image processing but without the emission of a lightbeam.

The document “OptiVeo: A Vision-Based Platform for Driving Assistance”,by P. Reilhac et al., from the SAE World Congress, 2006, describes apassive fog detection system, on the basis of cameras and imageprocessing, but not including the emission of a light beam.

The document EP 1 790 541, which is equivalent to U.S. PatentPublication 2007/01153357, which is incorporated herein by reference andmade a part hereof, describes a device for detecting dirty marks on thewindscreen of a motor vehicle, which uses two cameras and an imageprocessing system.

The document FR 2 847 367 describes a passive process and device todetermine the distance visibility in the present of an elementinterfering with visibility such as fog, although this does not compriseany emission of a light beam.

SUMMARY OF THE INVENTION

An object of the present invention is to provide means of detecting aphenomenon that interferes with visibility.

According to an initial embodiment, this object is achieved by a processthat enables a phenomenon interfering with visibility to be detected andcomprises the following stages:

the emission of a beam of light from a vehicle, this beam being emittedfrom a motor vehicle within the field of vision of a camera mounted inthe vehicle, and

the determination of the presence and the nature of the phenomenon thatinterferes with visibility on the basis of at least one image capturedby the camera.

As will be seen in detail below, such a process has the advantage ofanalysing such a phenomenon by means of an image captured by a videocamera. No complex electronic gadgetry is required. Moreover, the use ofa video camera is not very costly.

According to other non-limitative embodiments, the process also has thefollowing characteristics:

the nature of the phenomenon interfering with visibility is calculatedon the basis of the homogeneity and the granulometry of the phenomenonon the image. These two criteria can show whether the phenomenon is, forexample, fog or a spray of water;

the calculation of the nature of the phenomenon is made on the basis ofa tracking movement of the phenomenon. This enables a precisedistinction to be made between fog and a spray of water;

the beam of light is modulated. This permits the use of a multi-functioncamera which can be used to detect the presence of such a phenomenon andanother function such as a parking aid.

According to a second embodiment, the invention concerns a device forthe detection of a phenomenon interfering with visibility, comprising:

a light source emitting a beam of light from a vehicle, with this lightbeam being emitted within the field of vision of a camera mounted in thevehicle; and

a control unit to determine the presence and the nature of such aphenomenon on the basis of at least one image captured by the camera.

According to a third embodiment, the invention concerns a computerprogramming product having one or more sequences of commands that can becarried out by a data processing unit, the execution of the sequencessetting in motion the process in accordance with any of the abovecharacteristics.

These and other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Other characteristics and advantages of the present invention will bebest understood from the description and the non-limitative figuresincluding the following:

FIG. 1 represents a diagram of a non-limitative embodiment of thedetection process in accordance with the invention;

FIG. 2 is a schematic representation of a vehicle generating aphenomenon that interferes with visibility and has been detected by theprocess in accordance with FIG. 1;

FIG. 3 is a plan view of FIG. 2;

FIG. 4 is a first example of a captured image of a phenomenoninterfering with visibility that has been detected by the process inFIG. 1;

FIG. 5 is a second example of a captured image of a phenomenoninterfering with visibility that has been detected by the process inFIG. 1; and

FIG. 6 is a proposed non-limitative embodiment of a detection deviceenabling the process described by FIG. 1 to be implemented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

On a wet road, either as a result of wet weather or of fog, visibilityof the rear lights of a motor vehicle (car, lorry etc.) for a driver ina following vehicle may be affected by a phenomenon that interferes withthe visibility of another motor vehicle driver in the form, for example,of a spray of water thrown up from behind the vehicle. It is thereforeinteresting to assess the presence and the nature of this phenomenonthat interferes with visibility so that, if necessary, the vehicle'slighting and signalling systems can be switched on and/or increased(lights/headlights) so that the driver of the car behind can distinguishmore easily the signals of the vehicle in front.

The process of detecting such a phenomenon in accordance with theinvention allows such a form of detection and is described in anon-limitative embodiment in FIG. 1.

In this application, the detection is carried out using a detectiondevice mounted in a vehicle V comprising a video camera, described indetail below.

The detection process comprises the following stages as illustrated inFIG. 1:

the emission of a beam of light FX from a vehicle V, this beam of lightbeing emitted within the field of vision of the camera CAM of thevehicle V (stage EM(FX) or block 1 in FIG. 1), and

the determination of the presence and the nature of an interferencephenomenon G on the basis of at least one image I captured by the cameraCAM (stage ANAL_G(I) block 3 in FIG. 1).

It also comprises the following stage:

the capture of an image I by the camera CAM (stage ACQ_SQ(I) or block 2in FIG. 1).

A detailed description of these stages follows:

In the first stage 1), a beam of light FX is emitted from the vehicle V,this beam of light being emitted within the field of vision of thecamera CAM of the vehicle V.

In one non-limitative embodiment of the invention, the beam of light FXis a beam of infra-red light with a wave-length of around 850 nm. Thisprevents the creation of any undesirable lighting effects on the rear ofthe vehicle in the presence of an interference phenomenon G and therebyprevents discomfort on the part of the drivers behind. Moreover, itensures compatibility with the spectrum of detection of the camera CAMas it will be seen from a greater distance.

Furthermore, in another non-limitative embodiment of the invention, thebeam of light FX is narrow. In one non-limitative example it has anopening angle of 4°. This prevents any possible loss of power. It alsoproduces a concentration of energy in the beam of light FX and promotesthe detection of an interference phenomenon at much greater distances.

The beam of light FX is generated by a light source DIOD describedbelow.

FIG. 2 shows an example of a beam of light FX generated by a lightsource DIOD and emitted into the field of vision CAM_V of the camera CAMof the vehicle V. In the example shown, the beam of light FX is emittedbehind the vehicle V. Moreover, two sprays of water G1 and G2 are shownand illuminated by the beam of light FX.

FIG. 3 shows a plan view of FIG. 2. The position of the light sourceDIOD inside a rear light can be seen together with the position of thecamera CAM between the two rear lights.

In one non-limitative embodiment of the invention, the generation of thebeam of light FX is effected by activating the rear lights. This enablesthe driver to be sure of detecting an interference phenomenon such as aspray of water when it is raining or when the carriageway is wet andconsequently to adapt the lighting of his rear lights in accordance withthe nature of the interference phenomenon.

In a second stage 2), an image I is captured by the camera of thevehicle V.

As the video camera CAM is positioned, as shown, at the rear of thevehicle V, the captured image I represents the environment of thevehicle V within the field of the camera CAM and thus the rear of thevehicle V. In this way, an interference phenomenon G located at the rearof the vehicle V will be detected. In a non-limitative example, thecamera CAM is positioned in the vicinity of one of the rear lights ofthe vehicle V.

In this way, the beam of light FX emitted from one of the rear lights isdiffused through the particles of the interference phenomenon G insuspension in the atmosphere (after the movement of wheels along a wetcarriageway, for example). As the wavelength of this beam of light iscompatible with the analysis spectrum of the camera CAM, and as theparticles constituting the interference phenomenon G located within thefield of vision of the camera CAM, it is possible to capture an imagethat integrates the diffused light within the interference phenomenon G.

It will be noted that this stage, during which the images are captured,cannot be included in the process as described, but can be part ofanother process that is carried out in advance of the process described.

It will also be noted that the first and the second stages can becarried out in parallel.

In a third stage 3), the presence and the nature of a visibilityinterference phenomenon G can be determined on the basis of the image Icaptured by the camera CAM.

An analysis of this image I will enable:

the presence and the nature of the interference phenomenon (rain, fog)to be determined and thereby for the reduction of visibility of the rearsignalling system or of the front lights to be deduced, so as to be ableto compensate accordingly by increasing the intensity of the lights andthe signals in question (in the example, where the beam illuminates therear of the vehicle, the rear lights) or by activating the fog lights orby switching the headlights from a dipped beam to an undipped beam, and

the presence of an obstacle O to be revealed, and in particular, thepresence of a following vehicle so as to optimize the consumption ofadditional energy by the lights (and also to limit the effect of theseactions on the service life of filament bulbs).

Two non-limitative examples of an image I captured by the camera CAM areshown in FIGS. 4 and 5.

These images I give an indication of the diffused light during the nightwith a narrow beam of light FX. The beam is emitted from a light sourceDIOD situated on the left of the image I and above the camera CAM.

The white area represents the diffused night light with the beam oflight FX, while the shaded area marked B represents the surroundingenvironment, here the rear, of the vehicle V within the field of visionof the camera CAM that is not illuminated by the beam of light FX.

The example in FIG. 4 shows the environment at the rear of the vehicle Vin the presence of rain, without an obstacle O in the field of visionCAM_V of the camera CAM, with the image I revealing areas of water P1and P2, indicating the presence of an interference phenomenon G, such asa spray of water produced by aerodynamic turbulence behind the vehicleV.

The example in FIG. 5 shows the environment behind the vehicle V in thepresence of fog, with an obstacle O (for example, a following vehicle).

In the presence of fog PF, which is more homogenous and less moving thanareas of water, the beam of light FX appears more continuous. On thesame image, an external light source appears in the filed of vision, tothe right of the image I. This could be an obstacle O, such as theheadlight of a following vehicle, or alternatively a fixed light sourcein the countryside. The detection and characterization of this type oflight source in the image is simple if tracking methods are used, based,for example, on the detection of shadows so as to pick out the contoursof a following vehicle. As these methods are well known to the expert,they will not be described here.

In this way, using the images captured by the camera CAM, the followingcan be detected:

the presence and the nature of an obstacle O; and

the presence and the nature of an interference phenomenon.

With regard to the detection of an obstacle O, the information on thepresence of a following vehicle can be used to optimize the control ofthe intensity of the vehicle's signalling functions. In this way, it ispossible to adjust the intensity of the rear lights depending on thepresence or otherwise of a vehicle following closely behind (to preventdazzling). This will have the effect of increasing safety for bothdrivers in question.

It will also be noted that, at the rear of the vehicle, the intensity ofthe rear side lights is characterized by a number of standard points.According to one European Standard (EEC R7), the intensity of thesepoints varies between 0.05 cd and 4 cd minimum depending on the points.The maximum permitted is 12 cd for a single light and 17 cd for a set oflights. In this way, if water is detected, the intensity of the lightscan be increased, but if both water and the presence of a driver closebehind are detected, the intensity of the lights can be increasedaccordingly (that is to say, less than would be the case in the absenceof this vehicle so as to reduce the dazzle and less than in the presenceof a more distant vehicle).

With regard to the detection of a visibility interference phenomenon G,the characterization of the nature of this phenomenon is based on thehomogeneity and the granulometry of the diffused light. It is because ofthese two parameters that a distinction can be made between water andfog.

The advantage of being able to discriminate between water and fog hasthe effect of being able to activate a particular form of signalling inthe presence of fog, that is to say, the use of the fog lights, orincreasing the intensity of the rear lights in the event of a spray ofwater, for example.

It will be noted that in the case that there is a need to establishwhether the phenomenon is a mixture of spray and rain, the additionaluse of a rain sensor is possible. This sensor can also confirm that therainfall is regular.

The manner of determining the homogeneity of the diffused light isalready known to experts. In a non-limitative example, it can be basedon an analysis of the texture of an image I by using a probabilisticapproach, such as co-occurrence matrices and more particularly itshomogeneity criterion. As this method is well known to the expert, itwill not be described any further here.

The determination of the granulometry (the attribute of the texture) ofthe diffused light is also known to the expert. In a non-limitativeexample, it can be based on an analysis of the texture of an image I byusing probabilistic approaches, such as co-occurrence matrices and/orfrequential approaches, the Fourier transform, breakdown into waveletsetc. As these methods are all known to the experts, they will not bedescribed any further here.

In this way, if, on the captured image I, there is neither theinterference phenomenon G nor an obstacle O to be seen, the beam oflight FX will not be seen on the image. However, if, on the capturedimage I, there is no interference phenomenon G, but there is an obstacleO, to be seen this obstacle can easily be illuminated and characterized.

If, on the captured image I, an interference phenomenon G but noobstacle O is to be seen, the interference phenomenon is illuminated andvisible.

If, on the captured image I, there is both an interference phenomenon Gand an obstacle O to be seen, both the interference phenomenon G and theobstacle O will be illuminated and visible.

In the event of the presence of an interference phenomenon G, if, on thecaptured image I, the beam of light FX reveals non-homogenous zones forwhich the texture (indicated by the granulometry) is not smooth, it canbe concluded that there are areas of water present (as for example in awet carriageway with or without rain). At this moment, the intensity ofthe vehicle's lights can be increased.

If, on the captured image I, the beam of light FX reveals a continuoushomogenous zone for which the texture (indicated by the granulometry) issmoother, it can be concluded that fog is present (unless it is finerain that is present without the formation of spray). At this moment,the fog lights can be switched on.

In one non-limitative embodiment of the invention, the movement of theinterference phenomenon G on a sequence SQ of captured images can betracked in order to assist the characterization of the nature of thephenomenon. In this way, in the event of an interference phenomenon G,such as fog, no movement will be detected on the sequence SQ of thecaptured images I, whereas in the case of an interference phenomenonsuch as water, movement will be detected. This process is based on thetracking of zones illuminated on the sequence SQ of images I. As thistracking process is already known to experts, it will not be describedhere.

This tracking process is especially useful for distinguishing betweenfog and water in cases where no spray of water is generated (forexample, in cases of fine rain) or if the vehicle is travelling at lowspeeds. In this case, the captured image I presents a continuoushomogenous zone.

In a fourth stage 4), once a visibility interference phenomenon G hasbeen detected and its nature has been defined, an appropriate processingCD can be carried out in real time on the vehicle V.

In non-limitative examples, this can involve:

an automatic adaptation of the vehicle's V lighting system in relationto the indications on the nature of the interference phenomenon G byincreasing the intensity of the fog lights. In addition, account can betaken of the presence of the obstacle O as indicated above; or

the sending of an alarm system to the driver of the vehicle V, so thathe himself can adjust the intensity of his lights, for example byswitching on or increasing the intensity of his fog lights; or

the automatic switching on of the vehicle's lights (in the examplegiven, the rear signalling system, that is to say, the tail-lights andthe fog lights).

It will be noted that this fourth stage is carried out as and when thevideo images are processed by the process described above. In this way,the appropriate processing CD, such as, for example, the automaticadaptation of the rear lights, is carried out in real time, since it iseffected each time an interference phenomenon is detected, with adetection taking place with every capture of an image I.

The process according to the invention is implemented by a detectiondevice DISP shown in FIG. 6.

This DISP device comprises:

a light source DIOD emitting a beam of light FX from a vehicle V, withthis beam of light being emitted into the field of vision of a cameraCAM of the vehicle V; and

a control unit UC to establish the presence and the nature of avisibility interference phenomenon G on the basis of at least one imagecaptured by the camera CAM.

In addition, the control unit UC enables the light source DIOD and thecamera CAM to be controlled and also ensures the control (automaticadaptation of the vehicle's lights, automatic switching of the vehicle'slights) of the operation of the appropriate processing CD stage.

In one non-limitative embodiment of the present invention, the detectiondevice DISP can also include the video camera CAM enabling an image I tobe captured a illustrated in FIG. 6. It will be noted that in this casethe control unit UC can also be located in the video camera CAM.

The light source DIOD and the camera CAM are described in greater detailbelow.

The Light Source DIOD.

The light source DIOD is a diode of the LED type. In othernon-limitative embodiments it may be a laser diode, OLED, a halogen lampwith a light concentrator etc. or any other source capable of emitting abeam that is compatible with the camera CAM, as will be seen below.

In one non-limitative example, it is placed inside the vehicle'slighting and signalling system (in the example used, a rear light of thevehicle V, because of the additional protection afforded by the glasslight housing) or on the vehicle in the area of the lighting on thevehicle registration plate or on the lid of the rear hatch etc., all ofthese positions being ideally suited to detect the presence of aninterference phenomenon G, generated for example by one of the rearwheels. In fact, in view of its size (in the range of a cm³), a beam oflight generator, comprising the infra-red light source DIOD, plus anoptical projection system, is easy to incorporate into the lighting andsignalling system of a vehicle—in the example given, for instance, inthe rear light. Moreover, an electronic control system (steering thelight source DIOD and the camera CAM) can be placed in the rear part ofa light housing, which frequently has the necessary room.

The Camera CAM

This camera is, for example, of the type VGA with the definition 640*480(in other words, a captured image I comprising 8 bits (per pixel) with640 columns and 480 lines) and comprises a lens (not shown) for thispurpose. The image I that is captured in this way is in full resolution.

In a non-limitative example, the video camera CAM will capture 10 imagesper second. It will be noted that a sequence of images SQ is made up ofbetween twenty and a hundred or so images, depending on speed of travelof the vehicle V.

Evidently a different type of camera with a different resolution can beused.

It will be noted that the camera CAM being used to detect the presenceof an interference phenomenon G must be sensitive to the wavelength usedfor the beam of light FX. Again, in a non-limitative example, cameras ofthe type CMOS or CCD may be used, as these are traditionally employed inmotor vehicle applications because they are silicon based and have aresponse spectrum of between 400 nm and 1100 nm approximately (thewavelength range seen by the camera). This response spectrum is thuscompatible with an infra-red beam of light FX. In this way, the beam oflight FX will be seen by the camera CAM because it has a wavelength thatlies within the range of wavelengths at which the camera CAM issensitive.

Furthermore, the field of vision CAM_V of the camera CAM cuts the beamof light at a fairly short distance (between 1 and 5 meters) from theemission source DIOD of the beam of light FX. This enables preciseinformation to be obtained on the interference phenomena G situated, inthe example shown, at the rear of the vehicle, and is certain to detectthe presence of such a phenomena and in particular a spray of water.Moreover, the range of the field of vision CAM_V of the camera isdetermined in such a way as to cover an area in which an interferencephenomenon G (for example a spray of water) could be generated. In anon-limitative example, this is in the range of 20 meters.

It will be noted that all the stages of the process described above areeffected for one or more (sequence SQ) captured images I by the videocamera CAM—and this in real time. That is to say, that all the stagestake no more than 1/10 of a second in the example of a sequence of 10images per second captured by the camera CAM.

It will also be noted that the implementation of the detection processdescribed above can be carried out using a micro programmed softwaredevice, a cabled logical system or by hardware electronic components.

In this way, the detection device DISP can comprise a computer programproduct TG having one or more sequences of instructions that can becarried out by an information processing unit such as a microprocessor,the processing unit of a microcontroller, an ASIC or a computer etc.,with the execution of the said sequences of instructions effecting thestart-up of the process described.

A computer program PG of this type can be stored in a non-volatilememory of the ROM or EEPROM or FLASH type. The computer program can bestored in the memory at the works or loaded or remote loadedsubsequently. The sequences of instructions can be sequences of machineinstructions or again they may be sequences of a control languageinterpreted by the processing unit at the moment they are given.

In the non-limitative example in FIG. 6, the computer program PG isstored in the memory of the control unit UC of the device DISP.

Evidently, the description of the process is not limited to theembodiments described above. In this way, in another non-limitativeembodiment, the beam of light FX that is emitted may be modulated. Forexample, it might be envisaged that the light is issued at every “n”images captured by the camera CAM and then comparisons or abstractionsare made (simple image processing operations) between the images withand without modulated light. As a result of thesecomparisons/abstractions, it is simple to distinguish the beam of lightFX in such a way as to study the interference phenomena G that becomevisible as described above. Insofar as “n” is high (for exampledisplaying 29 images without modulated light and the 30th modulated in asystem capturing 30 images/second) it is possible to superimpose thefunction “detection of interference phenomenon” onto another functionsuch as a parking aid function, without changing the detection functionof the interference phenomenon.

Evidently, what was described above for the example of a beam of lightFX emitted in order to light up the rear of a motor vehicle V could alsoapply to a beam of light FX to light up the front of a motor vehicle Vin order to detect a visibility interference phenomenon at the front ofthe vehicle. In this case, the vehicle V is fitted with a camera CAMpositioned in the front.

In this case, after detecting a visibility interference phenomenon G atthe front of the vehicle V, in non-limitative examples, the appropriateprocessing CD tracking the vehicle V in real time can be effect by:

automatically adapting the intensity of the front headlamps of thevehicle V in relation to the information provided on the nature of theinterference phenomenon G by increasing the intensity of the headlamps(dipped or undipped) and/or by activating the fog lights. In addition,the presence of an obstacle O as indicated above will be taken intoaccount; or

automatically switching headlamps from their dipped to their undippedmode; or

sending an alarm signal to the driver of the vehicle V so that hehimself can increase the intensity of his headlamps if he can, forexample, in order to switch on to increase the effect of his fog lights.

Furthermore, adjustments could be made to enable the appropriateprocessing CD also comprises a system whereby the detection informationcan be transmitted to other systems within the vehicle V, such as forexample, a front camera that can track the white lines on the road. Thecamera could thus be warned that the road ahead is wet and if necessary,the intensity of the headlamps could be increased to ensure that thewhite lines in the road can be clearly perceived.

In this way, the present invention has the following advantages:

it can enable the presence of a spray of water to be detected, so thatthe rear lights can be appropriately adapted;

it can enable the nature of an interference phenomenon to be determined.In this way, in the event of fog, the foglights are switched on, whereasin the event of a spray of water, the intensity of the rear lights canbe adjusted;

it enables a visibility interference phenomenon, which could begenerated by the rear wheels of a vehicle, such as a spray of water, tobe detected. It can also distinguish between a spray of water (aphenomenon generated by the vehicle itself) and fog (a phenomenon notgenerated by the vehicle);

it enables the presence of an obstacle such as a following vehicle to bedetected and also its nature:

in the event that there is no such obstacle, the level of the rearlights is increased (if an interference phenomenon is detected);

in the event that an obstacle is detected, the level of intensity of thelights is increased in such a way that the driver of the followingvehicle is not dazzled or prevented from seeing the vehicle in front ofhim. This also has the effect of consuming less and thereby savingenergy;

it ensures that there is no confusion between an interference phenomenonand an obstacle, such as a following vehicle;

it prevents two cameras having to be used, one for the detection of aninterference phenomenon and another for use as a parking aid. In thisway, two functions can be carried out by the same camera, which ismulti-functional. The invention is economical, because the additionalcost of the function for the detection of an interference phenomenon islimited to the generation of the beam of light and the processing of theimages with this latter being able to use the same hardware support asthe parking aid; and

it can be easily integrated into a lighting and signalling system, suchas a sidelight or a headlamp (generator of light, camera) without havingany means of installation impinging on the bodywork of the vehicle.

While the forms of apparatus herein described constitutes preferredembodiments of this invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

1. A process for the detection of a visibility interference phenomenoncomprising the following steps: emission of a beam of light from avehicle, said beam of light being emitted into a field of vision of acamera of the vehicle; and determining the presence and the nature of avisibility interference phenomenon on the basis of at least one imagecaptured by the camera; wherein the determination of the nature of thevisibility interference phenomenon is effected on the basis of ahomogeneity of said visibility interference phenomenon on the image. 2.The detection process according to claim 1, wherein the determination ofthe nature of the said visibility interference phenomenon is effected onthe basis of the homogeneity and the granulometry of the visibilityinterference phenomenon on the image.
 3. The detection process accordingto claim 1, wherein the determination of the nature of the visibilityinterference phenomenon is effected on the basis of a tracking movementof the said interference phenomenon.
 4. The detection process accordingto claim 1, wherein the beam of light is modulated.
 5. A detectiondevice for a visibility interference phenomenon comprising: a lightsource emitting a beam of light from a vehicle, with this beam of lightbeing emitted within the field of vision of a camera of the vehicle; anda control unit to determine a presence and a nature of the visibilityinterference phenomenon on the basis of at least one image captured bythe camera; wherein said control unit determines said nature of thevisibility interference phenomenon on the basis of the homogeneity ofthe visibility interference phenomenon on the image.
 6. The detectiondevice according to claim 5, wherein said detection device comprises acomputer program product comprising one or more sequences ofinstructions that can be carried out by an information processing unit,the carrying out of the said sequences of instructions being wherein thecomputer program enables the process of: emission of a beam of lightfrom a vehicle, said beam of light being emitted into a field of visionof a camera of the vehicle; and determining the presence and the natureof a visibility interference phenomenon on the basis of at least oneimage captured by the camera; wherein the determination of the nature ofthe visibility interference phenomenon is effected on the basis of ahomogeneity of said visibility interference.
 7. The detection processaccording to claim 2, wherein the determination of the nature of thevisibility interference phenomenon is effected on the basis of atracking movement of the said interference phenomenon.
 8. A detectiondevice comprising: at least one camera mounted on a rear of a vehicle; acontrol coupled to said at least one camera for capturing an imagebehind the vehicle; said control being adapted to determine the presenceof at least one of rain or an obstacle in response to the homogeneity ofthe visibility interference phenomenon.
 9. The detection deviceaccording to claim 8, wherein said control bases the homogeneity of thevisibility interference and granulometry of diffused light.
 10. Thedetection device according to claim 8, wherein said detection devicefurther comprises a diode light source coupled to said control, saiddiode light source generating a light beam that is compatible with saidat least one camera.
 11. The detection device according to claim 10,wherein said diode light source generates said light beam when rearlights on said vehicle come on.
 12. A process for the detection of avisibility interference phenomenon comprising the following steps:emission of a beam of light from a vehicle, said beam of light beingemitted into a field of vision of a camera of the vehicle; anddetermining the presence and the nature of a visibility interferencephenomenon on the basis of at least one image captured by the camera;wherein the determination of the nature of the visibility interferencephenomenon is effected on the basis of a homogeneity of said visibilityinterference phenomenon on the image whenever rear lights on saidvehicle are on.
 13. The detection device according to claim 8, whereinan intensity of rear lights on said vehicle is adjusted in response to adetection of an obstacle.